title: Accurate analysis of the change in volume, location, and shape of metastatic cervical lymph nodes during radiotherapy.
abstract: OBJECTIVE
  To establish a method for the accurate acquisition and analysis of the variations in tumor volume, location, and three-dimensional (3D) shape of tumors during radiotherapy in the era of image-guided radiotherapy.
  
  
  METHODS
  Finite element models of lymph nodes were developed based on computed tomography (CT) images taken before the start of treatment and every week during the treatment period. A surface geometry map with a volumetric scale was adopted and used for the analysis. Six metastatic cervical lymph nodes, 3.5 to 55.1 cm(3) before treatment, in 6 patients with head and neck carcinomas were analyzed in this study. Three fiducial markers implanted in mouthpieces were used for the fusion of CT images. Changes in the location of the lymph nodes were measured on the basis of these fiducial markers.
  
  
  RESULTS
  The surface geometry maps showed convex regions in red and concave regions in blue to ensure that the characteristics of the 3D tumor geometries are simply understood visually. After the irradiation of 66 to 70 Gy in 2 Gy daily doses, the patterns of the colors had not changed significantly, and the maps before and during treatment were strongly correlated (average correlation coefficient was 0.808), suggesting that the tumors shrank uniformly, maintaining the original characteristics of the shapes in all 6 patients. The movement of the gravitational center of the lymph nodes during the treatment period was everywhere less than ±5 mm except in 1 patient, in whom the change reached nearly 10 mm.
  
  
  CONCLUSIONS
  The surface geometry map was useful for an accurate evaluation of the changes in volume and 3D shapes of metastatic lymph nodes. The fusion of the initial and follow-up CT images based on fiducial markers enabled an analysis of changes in the location of the targets. Metastatic cervical lymph nodes in patients were suggested to decrease in size without significant changes in the 3D shape during radiotherapy. The movements of the gravitational center of the lymph nodes were almost all less than ±5 mm.
authors.affiliation: Graduate School of Engineering, Hokkaido University, Sapporo, Japan. takao@mech-me.eng.hokudai.ac.jp
authors.forename: Seishin
authors.initials: S
authors.lastname: Takao
authors.forename: Shigeru
authors.initials: S
authors.lastname: Tadano
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Taguchi
authors.forename: Koichi
authors.initials: K
authors.lastname: Yasuda
authors.forename: Rikiya
authors.initials: R
authors.lastname: Onimaru
authors.forename: Masayori
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Gerard
authors.initials: G
authors.lastname: Bengua
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Suzuki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D002277:Carcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy* / Q000556:secondary; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy / Q000556:secondary; D003116:Color; D005260:Female; D057918:Fiducial Markers; D020342:Finite Element Analysis; D006801:Humans; D008198:Lymph Nodes / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects*; D008207:Lymphatic Metastasis; D008297:Male; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D009333:Neck; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden / Q000528:radiation effects*